Add startup search option

[TIR44]

Fixes #389

Repro / motivation

moor already supports interactive search, but there was no CLI equivalent for tools such as delta to open a file with an initial search term ready for n / p navigation.

Fix

Added --search <pattern>:

• parses the startup search term from CLI args
• applies it through the existing pager search state on startup
• jumps to the first visible match when possible
• leaves the pager in normal viewing mode so n and p work immediately
• documents the option in the man page

Tests

• go test ./cmd/moor ./internal -run 'TestSearchOption|TestInitialSearch|Test152|TestScrollToNextSearchHit'
• go test ./...
• ./build.sh && MOOR_SKIP_INTERACTIVE_TESTS=1 ./test.sh